1. Field of the Invention
The present invention relates to a yarn feeding apparatus for feeding a knitting yarn, for knitting a fabric, to a weft knitting machine.
2. Description of the Related Art
Conventionally, a weft knitting machine 1 shown in FIGS. 24 and 25 has a yarn feeding apparatus 6 provided in a side cover 5 in order to feed a knitting yarn 4 to a yarn feeding port 3 when knitting a fabric 2. The yarn feeding apparatus 6 comprises a buffer rod 7 having a function of temporarily storing the knitting yarn 4, and a function of adding tension to the knitting yarn 4. The buffer rod 7 has a base end side 8 supported on the side cover 5 and can rock and displace a tip side 9 around the base end side 8. The tip side 9 of the buffer rod 7 pulls the knitting yarn 4 by virtue of a spring and is stabilized with energizing force of the spring balanced with a tensile force based on tension of the knitting yarn 4. A length measuring roller 10 serves to measure a length of the knitting yarn 4 to be fed from the yarn feeding apparatus 6 to the yarn feeding port 3. As a result of the measurement of the length of the knitting yarn 4, a stitch representing an amount of pull-in of a knitting needle pulled in through a carriage to knit the fabric 2 can be controlled such that an amount of consumption of the knitting yarn 4 is coincident with a predicted amount based on knitting data.
FIG. 24 shows a positional relationship of the yarn feeding port 3 in a state in which the carriage is moved toward the yarn feeding apparatus side of a needle bed in the weft knitting machine 1, and is then started to be moved away from the yarn feeding apparatus 6. FIG. 25 shows a state in which the carriage is moved to an end apart from the yarn feeding apparatus 6, and the yarn feeding port 3 is also moved over the fabric to an end on the side provided apart from the yarn feeding apparatus 6. In the weft knitting machine 1, an amount of demand for the knitting yarn 4 also fluctuates depending on the positional relationship of the yarn feeding port 3 with the fabric 2. In the conventional yarn feeding apparatus 6 in which the knitting yarn 4 is stored and tension is provided within an inclination of the buffer rod 7, the buffer rod 7 stores the knitting yarn 4 at a maximum with the yarn feeding port 3 reaching an end on the yarn feeding apparatus side of the fabric 2 as shown by a broken line of FIG. 24. When the knitting operation for a next course of the fabric 2 is started, the yarn feeding port 3 is moved in such a direction as to go away from the yarn feeding apparatus 6 by virtue of the carriage. Since the knitting yarn 4 is pulled, the inclination of the buffer rod 7 is reduced as shown by a solid line. As shown in FIG. 25, when the yarn feeding port 3 approaches the end of the fabric 2 on such a side as to go away from the yarn feeding apparatus 6, the amount of demand for the knitting yarn 4 is decreased and the inclination of the buffer rod 7 is increased again, as shown by a broken line, to pull in and store the knitting yarn 4 in a larger amount. The inclination of the buffer rod 7 corresponds to tension of the knitting yarn 4. In such a structure in which the inclination of the buffer rod 7 provides a tension and stores the knitting yarn 4, therefore, tension of the knitting yarn 4 fluctuates greatly during a middle of the knitting operation.
For example, Japanese Examined Patent Publication JP-B2 2541574 discloses conventional art in which tension is provided to a knitting yarn by using a member corresponding to the buffer rod 7 shown in FIGS. 24 and 25, and preliminary storage is carried out to cope with a sudden fluctuation, thereby suppressing a fluctuation in yarn tension while actively feeding a knitting yarn. Moreover, Japanese Unexamined Patent Publication JP-A 11-500500 (1999) aslo discloses conventional art in which rotation of a spinning wheel for feeding a knitting yarn is controlled prior to a sudden change in a demand for the yarn, thereby suppressing a fluctuation in yarn tension without using a member corresponding to the buffer rod 7 shown in FIGS. 24 and 25.
In the conventional yarn feeding apparatus 6 shown in FIGS. 24 and 25, the amount of demand for the knitting yarn 4 greatly fluctuates depending on a position of the yarn feeding port 3, and the yarn tension also fluctuates depending on the demand for the yarn by an operation for knitting the fabric 2 in the weft knitting machine 1. Also in conventional art, as described in the JP-B2 2541574, it is hard to cope with a sudden fluctuation in the amount of demand for yarn which results at the end of the fabric. In conventional art described in the JP-A 11-500500, it is expected that a countermeasure can be taken against a sudden fluctuation in the amount of demand for a knitting yarn. In this conventional art, however, it is necessary to wind the knitting yarn onto a spinning wheel. Therefore, a size of the spinning wheel is increased. In a weft knitting machine, a plurality of yarns are often used properly to knit a fabric so that a yarn feeding apparatus is to be provided for each yarn.
FIGS. 24 and 25 show that a precise amount of the knitting yarn 4 for the entire width of the fabric 2 is unknown even if the length of the knitting yarn 4, which has already been fed to the length measuring roller 10, is to be measured in order to feed the required knitting yarn 4 corresponding to knitting data of the fabric 2. More specifically, in FIG. 24 showing a data fetch starting position, it is possible to measure a precise length of the knitting yarn 4 only at a portion provided apart from the end of the fabric 2 by approximately several centimeters. In the case in which the buffer rod 7 is inclined from a state shown by a solid line to a state shown by a broken line, the amount of storage of the knitting yarn 4, which is increased with the inclination of the buffer rod 7, is also measured by virtue of the length measuring roller 10 so that the net amount of consumption of the knitting yarn 4 to be fed to the fabric 2 is unknown. Moreover, the amount of the knitting yarn 4 to be fed when the buffer rod 7 is returned from the state shown by the broken line to the state shown by the solid line cannot be directly measured by virtue of the length measuring roller 10. Also in FIG. 25 showing a data fetch ending position, the length of the knitting yarn 4 shown as a broken line is unknown. Also in the conventional art as described in JP-B2 2541574 and JP-A 11-500500, there is not disclosed a structure related to accurate measurement of the amount of demand for the knitting yarn.
It is an object of the invention to provide a yarn feeding apparatus capable of accurately feeding a knitting yarn, required for knitting, to a weft knitting machine while suppressing a change in tension against a sudden change in demand.
The invention provides a yarn feeding apparatus for feeding a knitting yarn to a yarn feeding port, depending on demand for the knitting yarn in a weft knitting machine, for knitting a fabric while moving the yarn feeding port in a direction of a width of the fabric, together with a knitting operation to be carried out by an advancing and retreating operation of a knitting needle based on knitting data. The yarn feeding apparatus comprises:
a main roller provided in a feeding path for the knitting yarn and partially coming into contact with the knitting yarn on a rotatable outer peripheral surface of the main roller;
a servo motor for rotating a rotary shaft of the main roller;
a driven roller for interposing the knitting yarn, in contact with the outer peripheral surface of the main roller, between the driven roller and the outer peripheral surface;
a driven mechanism for transmitting a driving force from the servo motor to rotate the driven roller at an equal circumferential speed interlockingly with respect to rotation of the main roller;
a buffer rod provided in a path through which the knitting yarn is to be fed, from a portion between the main roller and the driven roller, to the yarn feeding port of the weft knitting machine, wherein the buffer rod is capable of being rocked and displaced around a base portion thereof and serves to partially pull the knitting yarn from the path when a tip portion of the buffer rod is rocked and displaced toward one of two sides;
a spring for urging the buffer rod to one of the sides so as to pull the knitting yarn from the path by a predetermined length under a predetermined yarn tension;
a sensor for detecting a rocking and displacement state of the buffer rod, based on an origin of the tip portion of the buffer rod, when the knitting yarn is to be pulled from the path by the predetermined length, and for sending out a signal indicative of a result of the detection; and
a control device for proportion, integration and differentiation (PID) control of the servo motor based on the signal sent by the sensor,
wherein, before the knitting in the direction of the width of the fabric is to be started, the control device operates to supply a larger amount of the knitting yarn than that supplied when the tip portion of the buffer rod is positioned at the origin, carries out the PID control to include a differential component within a remainder side range from which a the tip portion is to be returned to a point corresponding to the origin when the knitting is started and demand for the knitting yarn is rapidly increased, and carries out the PID control so as not to include the differential component even if the the tip portion is placed on a remainder side or an insufficient side after the tip portion once passes through the point corresponding to the origin and is then transferred to an insufficient side range in which a length of the knitting yarn to be led out from the path is smaller than that to be led out when the tip portion is at the point corresponding to the origin.
According to the invention, the knitting yarn interposed between the main roller and the driven roller is fed to the yarn feeding port of the weft knitting machine. The knitting yarn is interposed between the driven roller and the main roller and is in partial contact with the outer peripheral surface of the main roller. The main roller is rotated by the servo motor. The rotating force of the servo motor is transmitted to the driven roller through the driven mechanism to be rotated at an equal circumferential speed relative to the speed of the rotation of the main roller. Since the knitting yarn is interposed between the main roller and the driven roller, having equal circumferential speeds, when the yarn is fed from between these rollers a force is not applied to the knitting yarn so that the knitting yarn can be supplied stably. The knitting yarn fed from between the main roller and the driven roller is led from the feeding path at the tip portion of the buffer rod. The buffer rod is urged by a spring such that the knitting yarn is led out by a predetermined length under a predetermined tension. The rocking and displacement state of the buffer rod is detected by virtue of the sensor, based on the origin to which the tip portion of the buffer rod is set at this time, and a signal representing the result of the detection is sent from the sensor to the control device. By such a control operation, an amount of the knitting yarn, larger than that supplied when the tip portion of the buffer rod is placed at the origin, is supplied before the knitting operation in the direction of the width of the fabric is started. The servo motor can be controlled by using the differential component for the PID control such that sufficient yarn is supplied corresponding to a sudden demand for the yarn in the case in which the tip portion of the buffer rod is set to the remainder side range apart from the point corresponding to the origin when the knitting operation is started and the demand for the knitting yarn is suddenly increased. After the tip portion of the buffer rod once passes through the point corresponding to the origin and is transferred to the insufficient side range, the differential component is not used for the PID control within both the remainder side range and the insufficient side range into which the tip portion is now located. Therefore, an oscillation can be prevented to stably carry out the control.
According to the invention, the servo motor can be controlled by using the differential component which can cope with a sudden increase in the demand for the knitting yarn at the start of the knitting operation, the knitting yarn required for the knitting can be supplied accurately, and furthermore, an oscillation can be prevented to stably carry out the control.
Moreover, the invention is characterized in that the control device PID controls the servo motor based on a change in position of the yarn feeding port with respect to the fabric and a change in amount of the knitting yarn which is calculated from the knitting data, such that the rocking and displacement state of the buffer rod is set within a predetermined range.
According to the invention, the control device PID controls the servo motor such that the rocking and displacement state of the buffer rod is set within the predetermined range. The control device can carry out control for pointing the knitting yarn such that the amount of feed of the knitting yarn is increased before the demand for the knitting yarn is actually increased, based on a change in position of the yarn feeding port with respect to the fabric and a change in amount of the knitting yarn which is calculated from the knitting data. The control for the pointing of the knitting yarn and the change in the rocking and displacement state of the buffer rod can operate such that the tension of the knitting yarn does not greatly fluctuate even if the knitting yarn is changed suddenly. The control is carried out such that the rocking and displacement state of the buffer rod is set within the predetermined range. Therefore, the amount of the knitting yarn to be led out by the buffer rod can be set within a constant range, the influence of the buffer rod on the amount of the knitting yarn to be fed to the fabric can be reduced, and the amount of feed of the knitting yarn can also be measured with high precision based on a driving state of the servo motor.
According to the invention, moreover, even if the amount of the demand for the knitting yarn fluctuates with the knitting operation of the fabric in the weft knitting machine, a fluctuation in yarn tension can be suppressed and the length of the knitting yarn to be fed to the fabric can be caused to correspond to the amount of the knitting yarn to be fed from the main roller with high precision.
Furthermore, the invention is characterized in that the control device carries out, with only the differential component, the PID control to include the differential component within the remainder side range, and carries out, with a proportion component and an integral component, the PID control to include no differential component.
According to the invention, although the proportion component is zero when the tip portion of the buffer rod passes through the point corresponding to the origin, the servo motor can be smoothly controlled by converting the differential component into the integral component to switch an output without a difference in speed.
According to the invention, moreover, tension of the knitting yarn can be properly controlled by continuously switching the PID control using only the differential component and the PID control using no differential component.
Furthermore, the invention is characterized in that the control device sets a gain into a high gain state having an excellent follow-up property while the tip portion of the buffer rod passes through the point corresponding to the origin from the remainder side range, first reaches a position in which an amplitude is maximum within the insufficient side range and returns to a predetermined range toward the point corresponding to the origin, and switches the gain into a low gain state having an excellent stability in such a position as to pass through the predetermined range and to return to the point corresponding to the origin.
According to the invention, the control can be carried out such that the state in which the gain of the control is high and the follow-up property is excellent is set in an early stage in which the knitting operation is started and the knitting yarn is started to be fed to the yarn feeding port, and the state in which the gain of the control is low and stable is set after an insufficient state of the knitting yarn is relieved and the tip portion of the buffer rod is started to be returned toward the point corresponding to the origin.
According to the invention, moreover, the state in which the gain of the control is high and the follow-up property is excellent can be set in the early stage of the knitting operation so that the insufficient state of the knitting yarn can be relieved rapidly. When the insufficient state of the knitting yarn can be relieved, the gain of the control can be decreased and stabilized.
Furthermore, the invention is characterized in that the control device carries out, in the high gain state, the PID control to include no differential component by setting, to be the insufficient side range, a range in which the tip portion of the buffer rod is first moved to the point corresponding to the origin from a position where a large amount of the knitting yarn is supplied before the knitting operation is started in place of the PID control to include the differential component by setting this range to be the remainder side range.
According to the invention, the control can be carried out such that the state in which the gain of the control is high and the follow-up property is excellent is set in the early stage in which the knitting operation is started and the knitting yarn is started to be fed to the yarn feeding port, and the state in which the gain of the control is low and stable is set after the insufficient state of the knitting yarn is relieved and the tip portion of the buffer rod is started to be returned toward the point corresponding to the origin.
According to the invention, moreover, it is possible to set the state in which the gain of the control is high and the follow-up property is excellent even if the knitting yarn is excessively pulled out after the knitting operation is started, thereby coping with a sudden increase in demand. When the insufficient state of the knitting yarn is relieved and the tip portion of the buffer rod is started to be returned toward the point corresponding to the origin, the control can be carried out such that the gain of the control is reduced and stability is enhanced.
Furthermore, the invention is characterized in that the control device carries out control for stopping rotation of the servo motor prior to such a time as to feed the knitting yarn to a knitting end where the knitting operation is completed on one of two sides in the direction of a width of the fabric such that the servo motor is actually stopped after the time to feed the knitting yarn to the knitting end, and a length of the knitting yarn to be reeled with an inclination of the buffer rod toward the insufficient side range before the knitting end is passed after a start of the control of the rotational stop is equivalent to a length of the knitting yarn to be stored by the return of the tip portion of the buffer rod to the point corresponding to the origin before the servo motor is actually stopped after the passage through the knitting end.
According to the invention, when the fabric which is being knitted reaches one of the knitting ends in the direction of the width, the knitting yarn is stopped from being until the knitting operation is subsequently started on the other side in the direction of the width. The rotation of the servo motor for feeding the knitting yarn cannot be carried out instantly but a constant time is required. Even if the servo motor is stopped when the position of the knitting yarn to be fed passes through the knitting end, the knitting yarn to be fed remains in a time taken to actually stop the servo motor and the buffer rod is rocked toward the point corresponding to origin to store the knitting yarn such that the feeding path for the knitting yarn can be prevented from being loosened.
According to the invention, moreover, sudden stop offset control for stopping the rotation of the servo motor is carried out prior to such a time that the knitting yarn is fed to the knitting end at which the knitting operation is completed on one of the sides of fabric in the direction of the width of the fabric. The servo motor which cannot be instantly transferred from a rotational state to a stopped state is actually stopped after the time to feed the knitting yarn to the knitting end is passed. By beginning stopping of the rotation of the servo motor before the knitting operation is completed, the knitting yarn can be prevented from being excessively fed before the servo motor is actually stopped. Before the knitting end is passed the control of the rotation stop is started, and the control is carried out such that the length of the knitting yarn to be reeled with the buffer rod inclined toward the insufficient side range is equivalent to the length of the knitting yarn to be stored by the return of the buffer rod toward the point corresponding to the origin before the servo motor is actually stopped after the passage through the knitting end. When the servo motor is finally stopped, therefore, the knitting yarn having a proper length can be stored in the buffer rod.
Moreover, the invention is characterized in that the control device carries out control to increase the amount of feed of the knitting yarn such that the tip portion of the buffer rod is set in the remainder side range apart from the point corresponding to the origin before a knitting operation for a next course is started when it is decided that the yarn feeding port leaves the knitting range in the direction of the width of the fabric based on a change in position of the yarn feeding port with respect to the fabric.
According to the invention, the knitting yarn can be stored up to the remaining range side on the tip portion side of the buffer rod in order to provide for a sudden increase in the demand for the yarn at the start of the knitting operation for one course of the fabric, and the control using the differential component within the remainder side range can be effective.
According to the invention, moreover, the amount of storage of the knitting yarn can be previously increased such that the control using the differential component is effective before the amount of the demand for the knitting yarn is suddenly increased.
Furthermore, the invention is characterized in that the control device carries out control to stop the servo motor when it is decided that the yarn feeding port is moved away from the knitting yarn feeding side with respect to the width of the fabric based on a change in position of the yarn feeding port with respect to the fabric, and that the position of an advancing and retreating operation of a knitting needle leaves an end of the width of the fabric based on the knitting data.
According to the invention, when the fabric is to be knitted over the side provided away from the yarn feeding side, tension of the knitting yarn can be maintained within a proper range without excessively feeding the knitting yarn.
According to the invention, moreover, the servo motor can be stopped to prevent the knitting yarn from being excessively fed during a stage in which the demand for the knitting yarn is eliminated.
Furthermore, the invention is characterized in that the control device calculates the amount of the knitting yarn for each knitting needle.
According to the invention, pointing control is carried out by calculating the amount of the knitting yarn for each knitting needle. Therefore, it is possible to reduce a fluctuation in tension applied to the knitting yarn when knitting the fabric.
According to the invention, moreover, it is possible to reduce a fluctuation in a yarn tension for each knitting needle to knit the fabric.
Furthermore, the invention is characterized in that the control device calculates the amount of the knitting yarn for plural knitting needles.
According to the invention, the amount of the knitting yarn is calculated for plural knitting needles. For example, therefore, it is possible to make the entire tension constant while changing the tension for each knitting needle, thereby making the best of a feature of the fabric for a knitting operation with a change in a regular amount of consumption of the yarn, for example, jacquard knitting.
According to the invention, moreover, it is possible to prevent the tension from being changed for plural knitting needles, thereby making the best of a feature of a pattern to be knitted.